1. Field of the Invention
This invention relates to a communications system for a position detector, which is effective when applied, particularly, as a communications system for a position detector for use in machine tools, automobiles, robots, etc.
2. Description of the Related Art
A position detector, which detects the position of a machine, is utilized in a numerical control (or NC) machine tool equipped with an NC device. The NC machine tool controls a drive section based on a signal from an NC control section to move the machine. The amount of movement at this time is detected by the position detector. Relevant detection data is inputted into the NC device via an A/D converter. That is, the NC machine tool exercises feedback control with the use of the position detector to control the position of the machine with high accuracy. Incremental output or serial communication, comprising digital pulse signals of A-phase or B-phase, is used as an output from the A/D converter to the NC device. These outputs (incremental output and serial communication) are presented only one-way from the position detector to the NC device.
JP-A-2000-315103 discloses an administrative system for an NC machine tool. In this administrative system for an NC machine tool, a personal computer is connected to a controller section of the NC machine tool via a network. A display of the personal computer indicates a plurality of operating icons which have functions conformed to control commands of the NC machine tool. These operating icons are selectable by a mouse. Furthermore, the operating state of the NC machine tool is examined and, depending on this operating state, the operating icon is prohibited from pointing to a command.
The above-mentioned incremental output is a general-purpose communications protocol for the NC device, and contains only positional information on the machine. The serial communication, on the other hand, is a communications protocol unique to the NC device, which is the receiver of communication from the position detector, and has no versatility. Moreover, data included in the serial communication has limited contents, such as a break in a wire. Thus, even the use of serial communication has posed difficulty in pinpointing the location of failure.
If mounting, adjustment, checking for failure, or the like is performed in the aforementioned NC machine tool, an operation for confirming settings of the position detector and an output signal from this detector is carried out. This operation is performed, with the connection between the position detector and the numerical control device being cut off and, in this state, a position indicator (counter device) dedicated for the position detector being connected to the position detector. That is, the numerical control device is once stopped, and the connection between the numerical control device and the position detector is cut off. In this state, the position detector and the position indicator are connected, and information displayed on the position indicator is confirmed. Thus, maintenance work itself has been complicated. After completion of the confirming operation, moreover, the connection between the position detector and the position indicator has to be cut off, and the position detector and the numerical control device have to be connected. This operation itself has also been complicated. With the above procedure, moreover, the numerical control device, which is a constituent of the system, is disconnected, and the position indicator, which is not a constituent of the system, is separately connected. Hence, there has been a possibility that the location of failure cannot be pinpointed.
With the administrative system for an NC machine tool described in JP-A-2000-315103, the control section of the NC machine tool, to which the personal computer is connected, differs according to various machine tools. Thus, the settings on the personal computer side have to be changed in conformity with the specifications of the control section. As seen here, the administrative system has not been versatile.
The present invention has been proposed in light of the above-described problems. It is an object of the invention to provide a communications system for a position detector, which is versatile, which can perform maintenance work in a state connected to a numerical control (NC) device, and which improves the accuracy of the maintenance work.